Electronic Supplementary Material (ESI) for ChemComm. This journal is The Royal Society of Chemistry 2018 Electronic Supplementary Information One-Dimensional MoO2-Co2Mo3O8@C Nanorods: A Novel and High Efficient Oxygen Evolution Reaction Catalyst Derived from Metal Organic Framework Composite Yanqiang Li, a, *, Haibin Xu, a Huiyong Huang, a Chao Wang, a Liguo Gao, a Tingli Ma a,b * a State Key Laboratory of Fine Chemicals, School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin Campus, Panjin 124221, China b Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu, Kitakyushu, Fukuoka 808-0196, Japan. *Corresponding author. E-mail address: tinglima@dlut.edu.cn; yanqiangli@dlut.edu.cn
Experimental section 1 Synthesis of MoO3, MoO3@ZIF-67 and MoO2-Co2Mo3O8@C nanorods The MoO3 nanorods were prepared according to the published procedure [31]. For a typical procedure, 1.4 g of ammonium heptamolybdate tetrahydrate was dissolved in 40 ml of mixed solution of 65% HNO3 and H2O with a volume ratio of 1:5. The solution was transferred into a Teflon-lined stainless steel autoclave and heated at 200 o C for 20 h. After cooling to room temperature, the product was filtered out, washed several times with ethanol and then dried at 70 o C for further use. For the synthesis of MoO3@ZIF-67 composite, 50 mg of MoO3 nanorods were dispersed in 40 ml of CH3OH solution and sonicated for 10 minutes. Then 217.5 mg of Co(NO3) 6H2O and 246 mg of 2-methylimidazole were added. The solution was transferred into a Teflon-lined stainless steel autoclave and heated at 70 o C for 3h. After cooling to room temperature, the product was filtered out, washed several times with methanol and dried at 60 o C for further use. The obtained MoO3@ZIF-67 was thermal annealed at 500 o C or 700 o C for 2h in flowing N2 atmosphere, and the obtained samples were denoted as MoO2- Co@C and MoO2-Co2Mo3O8 @C. For composition, ZIF-67 was also thermal annealed at 700 o C to obtain Co@C. Besides, Co3O4 was also prepared by thermal annealing ZIF-67 under air conditions at 450 o C comparison. for 2h for 2 Characterization The compositions of the catalysts were investigated by Powder X-Ray diffractions (PXRD) using a Riguku D/MAX 2550 diffractometer. Catalysts morphologies were characterized by Field Emission Scanning Electron Microscopy (FE-SEM, Nova NanoSEM 450). Transmission electron microscopy (TEM) and high resolution TEM images were obtained using FEI, Tecnai G2 F20 with an accelerating voltage of 200 kv. X-ray photoelectron spectroscopy (XPS) was conducted with ESCALAB 250Xi (ThermoFisher).
Pore structure was characterized by N2 sorption at -196 C (Quantrachrome Quadrasorb Si-MP) and evaluated by Quenched Solid State Density Functional Theory (QSDFT) model assuming slit-shaped pores. 3 Electrochemical measurements The catalytic tests were carried out in a standard three-electrode cell in O2 saturated 1 M KOH solution, using a platinum wire as the counter electrode and Ag/AgCl as the reference electrode. A glassy carbon disk (5 mm in diameter) was used as the working electrode, and the catalyst ink was pipetted onto it with a loading of 0.20 mg cm -2. The current densities were normalized to the geometric area of the glassy carbon electrode and the scan rate for the electrochemical measurements was 5 mv s -1. All potentials were referenced to reversible hydrogen electrode (RHE) scale by E (RHE) = E (Ag/AgCl) + 0.059pH V + 0.197 V. Figure S1 PXRD of the synthesized MoO3, ZIF-67 and MoO3@ZIF-67. The peaks at about 7.4 o, 10.4 o, 15-20 o, 22.5 o for MoO3@ZIF-67 are all peaks that only can be found in ZIF-67, demonstrating that ZIF-67 was assembled on the MoO3 nanorods successfully.
Figure S2 SEM images of the MoO3, MoO3@ZIF-67, MoO2-Co@C and MoO2-Co2Mo3O8@C. Figure S3 PXRD of the synthesized MoO2-Co@C ZIF-67 and MoO2-Co2Mo3O8@C.
Figure S4 SEM images of MoO3@ZIF-67 annealed at 900 o C. Figure S5 High-resolution TEM image of MoO2-Co2Mo3O8@C.
Figure S6 XPS survey of the MoO2-Co2Mo3O8@C. Figure S7 XRD of the Co3O4 synthesized by thermal annealing ZIF-67 under air condition and 450 o C.
Figure S8 Cyclic voltammetry curves of MoO3, Co@C, MoO2-Co@C and MoO2- Co2Mo3O8@C at different scan rate from 20 to 200 mv s -1.
Table S1 Summary for the properties of recent reported OER catalysts. Catalyst Electrolyte Overpotential @10 ma cm -2 / mv Tafel slope / mv dec -1 Reference MoO2-Co2Mo3O8@C 1 M KOH 320 88 This work CeO2/CoSe2 1 M KOH 310 44 1 CoP hollow polyhedra 1 M KOH 400 57 2 Co2P NPs 1 M KOH 310 50 3 NiCo2S4 NA/CC 1 M KOH 340 89 4 CoP/rGO-400 1 M KOH 340 66 5 CoSe2 1 M KOH 430 50 6 Co-Mo-B 1 M KOH 320 155 7 NiCoP/C 1 M KOH 330 96 8 CoSe2 1 M KOH 330 79 9 Mo N/C@MoS2 0.1 M KOH 390 72 10 Reference: 1. Y. R. Zheng, M. R. Gao, Q. Gao, H. H. Li, J. Xu, Z. Y. Wu and S. H. Yu, Small, 2015, 11, 182-188. 2. D. Zhou, L. He, W. Zhu, X. Hou, K. Wang, G. Du, C. Zheng, X. Sun, and A. M. Asiri, J. Mater. Chem. A, 2016, 4, 10114-10117. 3. M. Liu and J. Li, ACS Appl. Mater. Interfaces, 2016, 8, 2158-2165. 4. D. Liu, Q. Lu, Y. Luo, X. Sun and A. M. Asiri, Nanoscale, 2015, 7, 15122-15126. 5. L. Jiao, Y. Zhou and H. Jiang, Chem. Sci., 2016, 7, 1690-1695. 6. I. Kwak, H. S. Im, D. M. Jang, Y. W. Kim, K. Park, Y. R Lim, E. H. Cha and J. Park, ACS Appl. Mater. Interfaces, 2016, 8, 5327-5334. 7. S. Guptaa, N. Patela, R. Fernandesa, S. Hanchatea, A. Miotellob and D.C. Kotharia, Electrochimica Acta, 2017, 232, 64-71. 8. P. He, X. Yu and X. (David) Lou, Angew. Chem. Int. Ed, 2017, 129, 3955-3958. 9. X. Liu, Y. Liu and L. Fan, J. Mater. Chem. A, 2017, 5, 15310-15314. 10. I. Amiinu, Z. Pu, X. Liu, K. Owusu, H. G. Monestel, F. Boakye, H. Zhang and S. Mu, Adv. Funct. Mater., 2017,1702300.